My family has owned our 2000 Mercury Marquis buying it new for my mother in I believe April of 2000. She stopped driving it 4 years later getting into a accident with it that I had fixed for her before taking her license away because of Dementia/Alzheimers starting in and around 2004. The car still only has 36k miles on it today and has been my get around car. I don't drive it much but I won't part with it. For I am going to guess the last 4-5 years I have had on and off PO320 Code Readings for check engine light. Twice with this reading I read it could very well be a Bad Crankcase Sensor or Cam Sensor. I purchased one of each in the Dorman Brand the first time around. I first replaced the Cam Sensor a 10 minute Job. It made no difference the engine would start but not stay running. I next replaced the Crank Sensor and it cured the problem. At that point I pulled the Cam Sensor out again and replaced it with the Original Ford Cam Sensor since it was not needed. After that fix the car came up with the PO320 Code again 13 months later and wouldn't stay running so I purchased another Dorman Crankcase Sensor. It cured the problem. This 2nd Replacement of the Crank Sensor only lasted 8 months and I got the Code once more. At that point and from talking to mechanics I know I ended up buying a brand new Motorcraft Crankcase Sensor hoping this would finally cure the problem. RIght from the get go it starts up but after minutes it shuts the engine off. I then thought what do I have to loose let me also change out the Cam Sensor again so that now I have a new Motorcraft Crank Sensor and a New Dorman Cam Sensor. It start up nice. It ran for about 15 minutes and the motor shut off once again and it won't stay running. Based on all the reading I have done I examined the wiring harness as best I can going down to the Crankshaft Sensor. It looks perfect so I followed it up to where it goes up to the Coils. Took the top cover of the engine off and inspected all I can see thinking maybe a mouse might of chewed through wiring or something of that nature but everything looks good. Don't see any exposed wiring. Today I am going to get it started while it is cold and lift it up to try to move the wiring around going to the Crankcase Sensor while it is running to see if it makes the car miss. I will do the same with the wiring harness going to the Cam Sensor. A mechanic friend of mine told me to try this as a last resort before I need to have this car towed to a repair place who may see something I don't see or know something more then I do about the car that it could be. This is the reason I am here writing before I do that. Just curious if anyone else found they had a PO320 Code Reading on their Marquis and what cured their problem. Thanks ahead of time for any help here. I am at my Wits end with this headache. I haven't used the vehicle in months. It happened back in January and it was just too cold to work on it so I just used another one of my vehicles. Now I have the time being it is warm out so I been spending that time trying to find the problem along with other things I need to get done outside.

 

Replying to my own post since no one else has in the last 7 months since I posted it. I am back having the Code PO320 once again. This time I decided I am going to change the Speed Sensor out and check wires around the transmission where it is mounted. I looked this Speed Sensor up online and I am seeing 2 Speed Sensors. Not knowing which one I needed I ordered both of them. I guess I will find out once I get under the car and it is now December and it is cold out. Maybe I will be lucky and find a warm day were I can get under the car to see what is going on. It is not so easy anymore at almost 72 years old. I am guessing no one else on this forum ever had a PO320 Code come up with so many Grand Marquis and Ford Crown Vics on the road to chime in on the above post. Disappointing.

 

Sorry for the delayed response -- I'm 84, and don't move around too fast these days . ;>)
Regarding your PO320 Code -- You changed the Sensors because Bad Sensors can cause that problem -- but the problem is still there.
The source of your problem is probably in the ECM (Engine Control Module), which sends the ENGINE SPEED SIGNAL to those Sensors.
Remember, after you replaced the Sensors, the car started and ran -- but died later. That would indicate that the Sensors were not the problem, and to look elsewhere.
If the Crank and Cam Sensors were bad, the car Would Not Start.
What you have now is looking like the Engine Speed Signal is not being sent to the Sensors, making you think that the Sensors are at fault.
You MAY have to replace the ECM.
Good Luck !!
1995 Grand Marquis Restoration - Mercury Forum - Mercury Enthusiasts Forums (1)

 

Actually changing the Crank Sensor every time in the beginning of this problem solved the problem but only for a limited time I believe the first time it lasted maybe 13 months and the 2nd time about 8 months before the Check Engine Light came on again and the car would start but not stay running very long. I believe I must of mentioned it above in my beginning post. I would have to pull over and let it sit for a bit then give it another try to get the car home. Some times working brakes and gas pedal with 2 feet to keep it running to get the car home. Back in May of 2022 when I wrote this post the problem had happened once again with the PO320 Code coming up. That is when I decided to put a Genuine Motorcraft Crank Sensor in the car thinking maybe Dorman Crank Sensors were not made very well. It lasted all this time from last May to about a week or two when the car started acting up again throwing the PO320 Code again and not wanting to stay running. This is where I am today. I did so some searching on the Net about a ECM going bad. It mentioned about a Code Showing for a BAD ECM. I have yet to get a code showing it so I don't believe the ECM is bad at this point.

 

Perhaps you can find an answer here:
https://www.yourmechanic.com/article...-jamahl-walker
Good Luck !!

 

Thanks but I exhausted plenty of searches over the last 2 years or so including the link you just provided to me and coming to this forum. As you can see you were the only one who answered my post here. The link you gave me was one of those I read and reread a number of times. I even tried You Tube but it was no help. Being it is Winter time now and it is cold out I haven't gotten under the car as of yet to change out the Speed Sensors as a process of Elimination and to check their wiring for any rips or damage. At almost 72 years old it is to much for me to deal with the Cold in the month of December. Luckily I have other ways to get around and don't have to depend on my Merc. I own other vehicles. At my age I don't drive that much anymore like I use to anyway. Thanks again for trying to help me.

 

Sorry I couldn't be of help -- I know what you mean about monkeying with the cars in cold weather -- I'm 84, and still do my own work.
If ya ever solve that problem, please let us know.
Good Luck, and HAPPY NEW YEAR !!

 

Have you had the car professionally scanned? It is worth the money.